1. Field of the Invention
This disclosure is directed to a nanocrystal light-emitting diode with improved structural stability. Exemplary embodiments of the present invention relate to a nanocrystal light-emitting diode with improved stability which comprises an excitation source, a nanocrystal-containing light conversion layer and an air layer formed therebetween to be exposed to the outside.
2. Description of the Related Art
In recent years, light-emitting diodes (“LEDs”) covering the entire visible spectrum, including red, green and blue, have been developed, and their applications have been extended to light sources for lighting systems and displays. Particularly, a white light-emitting diode is known to have a structure in which red, green and blue light-emitting diodes are simultaneously driven or a light-converting material is employed to convert the emission wavelengths of a light-emitting diode as an excitation source to different wavelengths. In the most generally available structures employing light-converting materials, a YAG phosphor emitting yellow light in a broad spectral range is applied to a blue LED chip, or a mixture of red and green phosphors is applied to achieve improved color purity. However, white light-emitting diodes employing inorganic phosphors developed hitherto have difficulty attaining satisfactory performance characteristics in terms of efficiency and color purity, compared to white light-emitting diodes in which red, green and blue light-emitting diodes are simultaneously driven to achieve white light emission. To overcome these limitations, semiconductor nanocrystals, which are known as materials with high luminescence efficiency and good color purity, have recently attracted much attention as novel light-converting materials for light-emitting diodes. Semiconductor nanocrystals absorb light over a broad spectral range and emit light of wavelengths corresponding to specific band gaps. Based on these advantages, the use of semiconductor nanocrystals enables the fabrication of white light-emitting diodes having emission wavelengths which can be controlled without being greatly affected by the wavelengths of particular excitation sources and having superior color purity to achieve high color reproducibility. Nonetheless, current studies on the application of semiconductor nanocrystals to light-emitting diodes still remain at the early stages and the precise mechanisms of many phenomena of the semiconductor nanocrystals is not established. In addition, semiconductor nanocrystals are smaller in size and are more susceptible to surface defects than inorganic phosphors. Because of these disadvantages, the luminescence efficiency and the emission wavelengths of nanocrystals may be negatively affected by heat generated upon driving the light-emitting diodes. A typical nanocrystal-containing light conversion layer is formed by applying nanocrystal/polymer resin composites to a light-emitting diode chip. However, the organic polymer constituting the light conversion layer is likely to be decomposed by heat generated upon driving or photons intensively emitted from the light source. The decomposition of the organic polymer will involve serious damage to the life and stability of the light-emitting diode.